Moist dynamics of tropical convection zones in monsoons, teleconnections and global warming

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1 Moist dynamics of tropical convection zones in monsoons, teleconnections and global warming J. David Neelin* Collaborators: Chia Chou**, Hui Su*, Katrina Hales*, Chris Holloway* *Dept. of Atmospheric Sciences & Inst. of Geophysics and Planetary Physics, U.C.L ** Inst. of Earth Sciences, Academia Sinica, Taiwan Leveraging a theoretical framework from convective qu equilibrium, moist static energy budget, +. Monsoon aspect: what limits seasonal movement of deep convection zones over continents? Tropical regional precipitation anomalies associated wit changes in deep convection zones: including drought regions in both El Niño & global warming cases. Mechanisms? Similarities?

2 Temperature T and Moisture q equations

3 Quasi-equilibrium schemes Manabe et al 1965; Arakawa & Schubert 1974; Moorthi & Suarez 1992; Randall & Pan 19 Posit that bulk effects of convection tend to establish statistical equilibrium among buoyancy-related fields Approach here depends on convection tending to constrain vertical structure of temperature field. For now: Smoothly posed convective adjustment Convective heating: (Betts 1986; Betts & Miller 1986) Q c = (T c - T)/τ c τ c time scale of convective adjustment T c convective profile; may interact with h b h b atm boundary layer (ABL) moist static energy T c typically moist adiabat or closely related Can be expanded about a reference state, T r c T c = T r c (p) + A(p) T 1c + higher order A(p) vertical dependence of the moist adiabat perturbation T 1 c incl. ABL adjustment by downdrafts to satisfy energy constraint Tends to reduce CAPE (convective available potential energy)

4 Vertical structure of temperature variations See also, e.g., Xu and Emanuel 1989; Fu et al 1994; Brown and Bretherton 1997; Sobel et al 2004 Regressions of Temp. on hpa Ave. Temp. (square Same for reversible moist adiabats over similar range (grey Daily, COARE Domain Monthly, tropical av Rawinsonde (4 mon) NCEP (2 yr) NCEP (24 yr) Courtesy, C. Holloway [Ciesielski et al (2003) data]

5 QE analytic Analytical solution under quasi-equilibrium convective constraints If T constrained to be close to QE temp T c ( p) T c c T! T! T c r + A 1 Primitive equations, momentum + hydrostatic: (% + D ) v + fk $ v = #'"! Td ln p + " t m p o p baroclinic pressure gradients have strongly constrained vertical structure p o p & ( ) c p d ln p# T + o % $ " & A 1 #! o

6 Analytic solution in deep convective regions (cont.) Vertical structure of baroclinic pressure gradients structure of baroclinic wind V 1. With barotropic component v = v o (x,y,p,t) + V 1 (p)v 1 (x,y,t) Continuity eqn. ω = Ω 1 (p) v 1 The moist static energy eqn. becomes ( t + D)(T ^ + q) ^ + M v 1 = F net where M is the gross moist stability M = Ω p h NB: Have not yet used convective closure on moisture. Neelin 1997; Yu et al 1998; Neelin and Zeng 200

7 Moist convection interacting with large-scale dynamic Convective Quasi- Equilibrium: Fast convective motions reduce Convective Available Potential Energy (CAPE) Constrains temperature through deep column Baroclinic pressure gradients Gross moist stability at large scales Refs: Arakawa & Schubert 1974; Emanuel et al 1994; Neelin & Yu 1994; Brown & Bretherton 1997; Neelin & Zeng 2000

8 Galerkin expansion Have approx. analytic solution for convective regions: Extend to full nonlinearity, non-convective regions, Use analytic solutions for leading basis functions in Galerkin expansion in vertical T = T r ( p) + K! k = 1 a k ( p) T ( x, y, t) + T Horizontal gradients of T matter; specify reference stat T r (p) to improve accuracy. Simplest case: 1 basis function in T, q Extra basis function for external mode 2 in v k R, Neelin and Zeng (2000)

9 Quasi-equilibrium Tropical circulation model: Primitive equations projected onto vertical basis functions fro convective quasi-equilibrium analytical solutions for Betts-Miller (1986) convective scheme, accurate vertical structure in deep convective regions for low vertical resolution GCM-like parameters but easier to analyze Radiation/cloud parameterization: Longwave and shortwave schemes simplified from GCM schemes (Harshvardhan et al. 1987, Fu and Liou 1993) deep convective cloud, CsCc fraction param. on precip Simple land model: 1 soil moisture layer; evapotranspiration with stomatal/root resistance dep. on surface type (e.g., forest, desert, grassland) low heat capacity; Darnell et al 1992 albedo

10 Dynamics of summer monsoon convective zones Seasonal movement of deep convection zones over continents Dynamical mechanisms mediating land-ocean contrast? Given the large insolation extending poleward over continents, w do deep convection zones not extend farther poleward? Do mechanisms affecting convection zones differ from continent continent? QTCM coupled to a mixed-layer ocean and simple land model Focus on dynamical aspects, less on surface type No-topography case emphasizes ocean-land contrast

11 Wind-based vs. precip.. regime-based monsoon definitio Freq. of surface wind direction; Khromov (1957); from Ramage (1971) Pronounced summer precip maximum; sfc low; upper level high and outflow, (e.g., Tang and Reiter 1984; Barlow et al 1998; Higgins et al 1998; Zhou and Lau 1998; Yu and Wallace 2000; ) i.e., characteristics of seasonal arrival of deep convection zone

12 Seasonal precipitation minus Annual Average JJA ave. Annual ave. DJF ave. Annual ave. mm/day

13 Latitude-height cross section at 90E from Bay of Ben across Tibetan Plateau (shaded regions are rising motion From Yanai et al. (1

14 Observed climatology January precfnet Precipitation Net Flux into the atmosphere

15 Observed climatology July precfnet Precipitation Net Flux into the atmosphere

16 QTCM climatology July (coupled to a mixed-layer ocean) Precipitation Net flux into atmosphere Low-level wind Upper-level wind QTCM1

17 Observed climatology July 4panel Precipitation Net flux into atmosphere Low-level wind Upper-level wind

18 Ventilation and the interactive Rodwell-Hoskins mechanism Chou, Neelin and Su 2

19 The ventilation mechanism import of low moist static energy air from ocean where heat storage opposes summer warming oceanic air: cooler and moisture is lower than convection threshold over warm continent import to continents by wind (including upper level jets) via advection terms in temperature and moisture equations Chou, Neelin and Su 2

20 The interactive Rodwell-Hoskins mechanism Rodwell and Hoskins (1996): imposed convective heating in Asia gives Rossby wave descent pattern to west, enhancing deserts. when convection is interactive: associated flow feeds back on heating, creating characteristic convection/dry region pattern» we emphasize feedback (convection baroclinic Rossby wave dynamics), hence:» interactive Rodwell-Hoskins (IRH) mechanism Chou, Neelin and Su 2

21 South American region case (observed albedo) Jan Precipitation Control Saturated soil moisture over South American region No ventilation: v q, v T set to zero over South American region No ventilation and no β-effect: f = constant in South American region (9S-56S - 70W-20W) Chou and Neelin 2

22 Refinement of experimental design 1. Consistent treatment of v χ : Irrotational (purely divergent) wind component v χ Non-divergent wind component v ψ No ventilation = suppress v ψ T, v ψ q Retains conservation property: since v ψ = 0 (v χ q + q v)da Domain

23 V2.3b Precipitation Control Asian region case July (1) Saturated soil moisture No ventilation: v q, v T set to zero No β-effect: f = constant QTCM v2.3 Chou and Neelin

24 V2.3b North American region case 1 July Precipitation Control Saturated soil moisture No ventilation: v q, v T set to zero No β-effect: f = constant in regio Chou and Neelin

25 V2.3b North American region case 3 July Precipitation Control No ventilation: v q, v T set to ze No T ventilation No q ventilation Chou and Neelin 2

26 African region case (observed albedo) ) July V2.3b Precipitation Control Saturated soil moisture No ventilation: v q, v T set to zero No ventilation and no β-effect: (red contour: albedo = 0.3) Chou and Neelin

27 African region constant albedo case ( Precipitation Control case (0.26 over Africa) ) Jul Saturated soil moisture No ventilation: v q, v T set to zero No ventilation and no β-effect: Chou and Neelin

28 Mechanisms affecting convective zones (S. American ca Ocean heat transport out of the tropics Ventilation and the interactive Rodwell-Hoskins mechanism

29 African northern summer monsoon climatology Albedo is leading effect on poleward extent of convection Dynamical mechanisms: affect margin of convective zone take over if albedo gradient is flattened

30 African monsoon & mid-holocene (6kaBP) green Saha Paleo Model Intercomp Proj (PMIP): orbital parameter change => small monsoon boundary shift (Joussaume et al 1999) rel to pollen data (Jolly et al 1998; Prentice & Webb 1998) LMD and ECHAM GCMs with same interactive veg model yield different results (DeNoblet et al 2000) QTCM expts with grass-like albedo over Sahara (Su et al, in prep) & interactive vegetation (Hales et al, in prep) Ventilation opposes rise of moisture; may not increase enough to reach increase in trop temp. Reduced ventilation expts: e.g. reduce advection affecting q anomalies rel. to control; or reduce ventilation in control and 6kaBP cases

31 African mid-holocene 6kabp monsoon Schematic of QTCM - SVeg expts.

32 Mechanisms for regional precipitation anomalies teleconnections and global warming Tropical regional precipitation anomalies associated with changes in deep convection zone including drought regions in both El Niño & global warming cases. Mechanisms? Similarities

33 Observed anomalies during July-Nov 1997 Precipitation (mm/day) Tropospheric Temperature Neelin et al 2003; Neelin and Su 2004 su

34 QTCM anomalies forced by Pacific positive SST anomalies July-Nov 1997 Precipitation (mm/day) Tropospheric Temperature

35 QTCM POSPAC-Fluxes Surface temperature Net surface flux Net flux into atmospheric column

36 QTCM July-Nov 1997: Anomaly budget contributions1 Moisture convergence M q v (by divergent flow) Moist static energy divergence * M v * Gross moist stability M=M s M q is an effective stability that include partial cancellation of adiabatic cooling by diabatic heating

37 QTCM July-Nov 1997: Anomaly budget contributions2 Radiative cooling anom. (top of atmosphere) due to temp. anom. Mean wind advection of moisture anomaly v q '

38 ENSO teleconnections to regional precip.. anomalies Su & Neelin,

39 ENSO teleconnections to regional precip.. anomalies a small zoo of mechanisms with moist convective and clou radiative feedbacks Zeng & Neelin 1999; Giannini et al 2001; Su et al 2001; Bretherton & Sobel 2002 Chiang and Sobel 2002; Chiang et al 2002; Su and Neelin 2002; Neelin et al 2003 Neelin and Su 2004 subm

40 The upped-ante mechanism2 Margin of convective zone with v inward from dry region Neelin, Chou & Su,

41 QTCM experiments suppressing upped-ante mechanism Precipitation Anomalies Control Anomaly ( ) ' term suppressed in region: (v q) ' T ' contribution to CAPE

42 Other mechanisms Moist Static Energy transport by divergent flow M v Gross Moist Stability M = M s - M q, (M q inc. with moisture) Perturbation MSE budget + ocean mixed layer / land M v ' = M ' v (v q) ' c t T ' + F net' + (v T) ' Yields precip anoms as T ' q ' q ', M ' ; v ', q ' E ' etc. M q top P ' [ M (v q) ' + v( M ' ) c t T ' + ] s Upped-ante Anomalous GMS Rad cooling, (v T) ocean transp, GMS multiplier effect SST disequilibrium s

43 Mixed layer ocean in Atlantic: 1 st year vs equilibrium Precipitation anomalies Positive 1997 El Nino Jul.-Nov. SST anom in Pacific: tropical Atlantic 50m ML SST is adjusting Long term equilibrium with El Nino SST anom artificially sustained (anomalies relative to climatology of ML Atlantic, clim. SST elsewhere)

44 Global Warming case: GCM Precip. Anom. DJF precip. anom. Three GCM Greenhouse gas scenarios for rel. to clim

45 QTCM doubled CO 2 experiments Qflux mixed-layer ocean Dec - Feb Precip change Dec - Feb QTCM Precip climatology Neelin et al 2003; Chou & Neelin 2

46 QTCM doubled CO 2 experiments Moisture budget contributions 1 M q ' v Anomalous moisture convergence due to moisture anom. q ' (v q) ' Anomalous moisture advection

47 QTCM doubled CO 2 experiments Moisture budget contributions 2 M q v ' Anomalous moisture convergence due to anomalous divergence (GMS multiplier effect feedback )

48 The upped-ante mechanism1 Margin of convective zone with v inward from dry region Neelin, Chou & Su,

49 QTCM 2xCO 2 Expt.. suppressing change in moisture advection (testing the upped-ante mechanism) Experiment 2xCO 2 Precip. change (mm/day) Control 2xCO 2 Precip. change

50 Response to imposed T change in CAPE T ' =1.5 C added to temperature only inside convection scheme Mimicks 2xCO 2 moisture and regional precip response DJF Precip (W/m 2 ), surface temp, moisture (K), tropospheric mean tem

51 Anomalous Gross Moist Stability (M ' ) mechanism Moist Static Energy transport by divergent flow M v M = M s - M q increases with increasing moisture, tends to reduce M may partially compensate if cloud top rises M v ' + M ' v = F ' net - (v q) ' + reduced increases to compensate P ' v(-m ' ) M q M Mechanism increases convergence & precip. in strong convergence zones: rich-get-richer

52 QTCM 2xCO 2 Expt.. suppressing change in gross moi stability, M (testing the M ' mechanism) Experiment 2xCO 2 Precip. change (mm/day) Control 2xCO 2 Precip. change

53 Summary: Regional precip. Teleconn./global warmin tropical regional precipitation anomalies in ENSO teleconnect case a handful of contributing mechanisms 2XCO 2 case, mixed-layer ocean case set of mechanisms wi some cross-over to ENSO case the "upped-ante mechanism": substantial negative precip. anomaly regions in both cases drought occurs at margins of convection zones with climatologi wind inflow from dry zone into convection zone the "anomalous gross moist stability (M') mechanism": contributes positive precipitation changes in strong precipitation regions in global warming case (but theory for M' very poor) Surface heat fluxes & SST important only when SST is in disequilibrium ( t SST or ocean transport anom.)

54 Regional precip. anom.. relation to monsoon case v ψ (q, T) terms: strong impact on precip/precip anomalies d to role in moist static energy budget partial cancellation of adiab. cooling & diab. heating smal M q /M large GMS multiplier effect oppose precip in parts of trop convg zones & limit poleward ext role in upped-ante mechanism; involves QE to not QE transition role of QE mediation: moisture rel to T of free troposphere vs imported q F net : favorable but not sufficient in monsoon; small in land anom ocean heat storage & transport ocean land contrast in monso contrib. some Atl. negative precip. anoms. in ENSO case

55 Title page Last Slide ENSO teleconnections section Global warming case End show

56 Neelin 1997

57 Model Summary QTCM equations t v 1 + D V1 (v 0,v 1 ) + fk x v 1 = -κ T 1 - stress t v 0 = (barotropic component) ^ a 1 ( t + D T1 )T 1 + M S1 v 1 = Q c + Rad + H ^ b 1 ( t + D q1 )q 1 + M q1 v 1 = Q q + E Moisture sink and convective heating Q q = Q c = ε c (q 1 T 1 )

58 ENSO Composite (DJF) Zeng, Neelin and Chou 2000 QTCM1 V2.0

59 QTCM climatology January (coupled to a mixed-layer ocean) Precipitation Net flux into atmosphere Low-level wind Upper-level wind QTCM1

60 Observed climatology January 4panel Precipitation Net flux into atmosphere Low-level wind Upper-level wind

61 QTCM experiments suppressing various mechanisms Precipitation Anomalies Anomaly ( ) ' term suppressed in region: T ' radiative effects (v T) ' (surface stress) '